The present invention relates to mass spectrometry and, in particular, to a spectrometer providing variable and improved sensitivity.
In a typical mass spectrometer, particles, such as different molecular species, are ionized and accelerated in an electric field. The acceleration of particles having the same charge will be principally dependent on the mass of the particles and thus particles may be separated by mass according to their final velocity in the electric field. Differences in velocity may be detected by a time-of-flight detector positioned after a drift region or by passing the particles through a magnetic or electric field to separate them into curving trajectories determined by mass and velocity to be received by a spatial detector.
For a larger mass species, the relative difference in velocities between the particles becomes much smaller. For example, in biological molecules with a mass around 1000 amu with a 0.01 amu difference, the time of flight (TOF) separation, normalized to one of the species can be on the order of:
            Δ      ⁢                          ⁢      TOF              TOF      0        =      5.0    ×          10              -        6            
For a 1 m drift following a 25 kV acceleration potential, the time of flight of the reference species (TOF0) can be on the order of 14 μs. Distinguishing these two species thus requires a time resolution of 72 ps in the time-of-flight detector, a resolution equal to the time for light to travel less than an inch. A similar problem, albeit in the spatial dimension, occurs with a bending magnet/spatial detector system.